The present invention is related to devices and methods for monitoring the supply voltage and ground connections on an integrated circuit (IC) after mounting thereof on a circuit board, including at least one voltage monitor and means for reading out the result of monitoring.
Electronic integrated circuits of today require more and more parallel supply voltage and ground connections for maintaining sufficient supply voltage, in spite of the high transient currents typical for CMOS circuits manufactured according to the IC-technology of today. In the testing of individual circuit components there is a possibility of checking, by means of special circuit testing equipment, that each one of the voltage and ground connections is intact by the use of a fixture where the current in each power and ground lead can be measured.
This possibility does not exist for an electronic circuit board. Here all supply leads on all circuits are tied to supply nodes and individual currents cannot be measured. In addition there is the problem of checking that the decoupling capacitors included between voltage supply and ground planes have been correctly connected.
There are no particularly suitable methods today for checking the supply distribution networks when testing circuit boards if a considerable part of the supply network falls, e.g., an interruption of one of two parallel soldered connections, it is possible for a malfunction to occur when the board is tested. It can then be taken out for a (troublesome) fault finding procedure and repair. However, there is a great risk that the fault will not appear during the testing of the board, but "merely" leads to deteriorated noise margins, especially with many parallel supply pins. This will later lead to intermittent faults and a poor reliability of the system.
For the checking of supply pin connections it is already known to compare voltage at different places on a chip, e.g., between two ground pins, and read out the result via so-called boundary scanning, cf. Dirk van de Lagemaat, "Testing Multiple Power Connections with Boundary Scan", Electronic Design News, Mar. 2, 1990, pp. 127-130, which is incorporated here by reference. This technique requires considerable wiring, however, and relies on resistance differences in the board and the integrated circuit, that is in copper and aluminum, respectively. Dual sensors must be used here to guard against a break in any one of the supply pins. In addition, mean value formation and handling of small voltages are also required.